The Celtics’ power forward position is essentially a two-man job shared by Brandon Bass and Jared Sullinger. They are both undersized for the position, making rebounding more difficult against the game’s taller forwards.

That doesn’t help the Celtics’ quest to improve their rebounding. They rank last in the NBA in rebounding and last in rebounding differential, meaning not only do they lose the battle under the boards most nights, they lose it by a lot.

That wasn’t the case Sunday night against the Magic in Orlando, where the Celtics outrebounded an opponent for only the third time this season, 51-42. Bass and Sullinger combined for 18 rebounds, including 11 offensive, which has been a major weakness this season.

Bass and Sullinger were essentially pitted against each other in training camp, with Bass, last year’s starter, briefly losing his job to Sullinger, who impressed the coaching staff during training camp with his maturity and basketball savvy.

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Sullinger started several early games but Celtics coach Doc Rivers decided to make a switch following season-opening losses to Miami and Milwaukee. While Sullinger blended well chemistry-wise with the starting rotation, Rivers wanted more offense early in games and returned to Bass.

Both appear more comfortable in their current roles. Bass can provide offense off the pick-and-roll and an occasional inside bucket, while Sullinger has provided spark off the bench. His 8 points in 14 minutes were critical to the Celtics’ keeping and extending a lead in Friday’s win over the Oklahoma City Thunder.

Bass has struggled from the field this season, his customary pick-and-pop jumper has not fallen with the same regularity as last season but he said he wanted to make more of a concerted effort to rebound. In games Bass has managed to avoid foul trouble, he has been an effective rebounder. On Sunday, he wedged through the big bodies of the Magic, including former Celtic Glen Davis, to get a couple of key offensive rebounds that led to second-chance points.

“I think we have to be more assertive as a group to be more aggressive as far as rebounding and I was just trying to do my part,” Bass said. “[Sunday night] showed it was a little bit of progress [with rebounding]. We just have to keep going.”

Bass said during the preseason that he was willing to accept any role, but his responsibility as a starter is something he cherishes. He had not been a full-time starter at any point during his career and ended his tenure with the Magic in coach Stan Van Gundy’s doghouse.

So when there was speculation that he would be removed from the starting lineup in favor of Sullinger, Bass remained his reserved self. He said he never doubted his ability, just seeking an opportunity to display that he can be effective in the paint.

“I would say I’m building man, I’m building,” he said. “I think in order for me to get comfortable with the team, I’ve got to get comfortable with my individual game and then bring that together. And then I can say I’m more comfortable.”

Sullinger has similarities to Davis in that they are both bulky, undersized, and have their shots blocked often by taller opponents. Sullinger had his shot blocked twice against the Magic, but that didn’t stop him from creating space and attempting 12 shots.

“That doesn’t bother me,” he said. “I just have to keep on going and do whatever this team asks me to do. Getting your shot blocked is going to happen, you just have to keep coming back. That’s what I do. I am feeling more comfortable out there as the games go on.”

The Celtics planned for Darko Milicic to have a defensive and rebounding impact but he left the team because of the illness of his mother and was eventually waived. So they are depending more on Bass and Sullinger than probably expected.

The club has an available roster spot but Rivers said the team is in no hurry to sign another big man. There is also an obvious void at the backup point guard slot. So for now, the Celtics will go with what they have, a combination of feverishly working forwards who will have to use guile and speed to grab rebounds.

The numbers are beginning to improve while Bass and Sullinger are providing a solid one-two punch for a team that needs interior scoring.

“I think we have to rebound more as a group, but we’re getting there,” Sullinger said. “As a team we’re going to get better every day.”

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